Chapter 6 Chemical Reactions and Equations

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Chapter 6 Chemical Reactions and Equations

• 6.1 Chemical Equations
• 6.2 Types of Reactions
• 6.3 Nature of Reactions

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6.1 Chemical Equations

• Objectives
• Relate chemical changes and macroscopic
  properties.
• Demonstrate how chemical equations describe
  chemical reactions.
• Illustrate how to balance chemical reactions by
  changing coefficients.

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Recognizing Chemical Reactions

• Chemical reactions occur all around you and
  within you.
• Evidence
• Color change
• Odor
• Temperature change
• Gas production
• Precipitate

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Writing Chemical Equations

• Reactant- substance that undergoes a reaction,
  the starting substance(s).
• Product- the new substance formed from the
  reactants.
• Rust
• Iron and oxygen react to form Iron (III) oxide

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Writing Chemical Equations

• Word Equations
• Chemical Equations
• First lets practice writing formulas.
• You MUST be able to write formulas in order to
  write the equations

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Word Equation

• Word equation
• Vinegar Baking soda ? sodium acetate water
  carbon dioxide
• Can be using common names or the chemical names.
• Acetic acid sodium hydrogen carbonate ? sodium
  acetate water carbon dioxide
• Word equations are the simplest form

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Chemical Equations

• Uses the chemical formulas for the reactants and
  products.
• This is why you must be able to write formulas.
• Baking soda and vinegar
• HC2H3O2 NaHCO3 ? NaC2H3O2 H2O CO2

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Chemical Equations

• It is also important to know the state the
  compounds are in
• (g) gas
• (s) solid
• (l) liquid
• (aq) aqueous
• HC2H3O2 (aq) NaHCO3 (s) ? NaC2H3O2 (aq) H2O
  (l) CO2 (g)

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Equations and Energy

• Some chemical reactions require an energy input
  to occur
• Some chemical reaction produce energy
• Energy can be in the form of electricity (input),
  heat or light.
• Endothermic reaction- absorbs energy
• Exothermic reaction- gives off energy

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Balancing Chemical Equations

• Balanced equation for the reaction of iron and
  chlorine
• 2Fe (s) 3 Cl2 (g) ? 2FeCl3 (s)
• To balance an equation you must first find the
  correct coefficients- the number written in front
  of a reactant or product tells the smallest
  number of particles of the substance involved in
  the reaction.

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Steps for balancing equations

• Write the skeleton equation for the reaction.
• Count the atoms of the elements in the reactants.
• Count the atoms of the elements in the products.
• Change the coefficients to make the number of
  atoms of each element equal on both sides of the
  equation.
• Write the coefficient in their lowest possible
  ratio.
• Check your work.